MathDB

3

Part of 2010 Grand Duchy of Lithuania

Problems(1)

at a strange party, each person knew exactly 22 others

Source: 2010 Grand Duchy of Lithuania, Mathematical Contest p3 (Baltic Way TST)

10/3/2020
At a strange party, each person knew exactly 2222 others. For any pair of people XX and YY who knew each other, there was no other person at the party that they both knew. For any pair of people XX and YY who did not know one another, there were exactly 6 other people that they both knew. How many people were at the party?
combinatorics